In the old Shopify, when you edit a page in the theme customizer, you are editing the ‘default template’ for that page type.
For example, the product page layout — which will affect ALL products. Or the layout for all collection pages, all blog posts, etc..
But in Shopify 2.0, you can now duplicate the page that you customized, and save it as a different template, which you can then apply to individual products, collections, etc...
This is really useful if you have different types of products — maybe you sell gift cards or subscription products and you want the layout and information on these product pages to be different from your regular products.
In this case you can just create two (or more ) different product page templates.
Another common use is for different types of collection pages.
If you have a special collection that is on sale or promoting a newly launched product, you can give it a custom design with a large sale banner and promo blocks. While your other collections remain as they always were, with a more basic design using the default collection template.
Lastly, a very good use of this is to create sub-collections.
Creating sub-collections in Shopify 2.0
Shopify doesn’t officially have sub-collections in the way that other platforms do. All collections are the same ‘level’.
So if you wanted to mimic sub-collections for the sake of organization, customer experience, or SEO, it was always kind of difficult. You sometimes could do it with a navigation list , sometimes you needed to copy and paste code.
Luckily this is no longer the case — you can get it all done in the theme editor by using page templates and sections.
I highly recommend creating sub-collections now that it’s so easy, because they are great for SEO. Google’s algorithm loves to see pages organized by category and groupings of similar products on each of these pages.
You can find an in-depth tutorial on my Youtube channel — https://youtu.be/6xABjVe_wsc